Polycrystalline silicon rod and method of processing the same

ABSTRACT

A polycrystalline silicon rod according to present invention has a structure for hanging of polycrystalline silicon rods to each other end-to-end, so that the efficiency of melting polycrystalline silicon can be increased considerably. A polycrystalline silicon rod obtained by entirely or partially removing a peripheral portion from the rod to leave a central portion, and processing the central portion, preferably, the peripheral portion is removed by grinding in an amount corresponding to 10 to 60% of the diameter of the rod, and then subjected to groove-forming processing. This makes annealing unnecessary.

TECHNICAL FIELD

[0001] The present invention relates to a polycrystalline silicon rodhaving a coupling structure and to a method of processing the same. Moreparticularly, the present invention relates to a polycrystalline siliconrod having a structure that enables hanging of polycrystalline siliconrods to each other end-to-end safely and easily, and to a method ofprocessing such polycrystalline silicon rods, in which groove-formingetc. can be made stably without performing annealing treatment.Hereinafter, the term “polycrystalline silicon rod” may sometimes beabbreviated simply as a silicon rod including both of them.

BACKGROUND ART

[0002] Recently, monocrystalline silicon is produced mainly by theCzhochralski process (CZ process). This process dips a seed crystal in amelt composed of molten polycrystalline silicon to allow monocrystallinesilicon to grow around the seed crystal while drawing up the seedcrystal gradually in accordance with the growth to produce amonocrystalline silicon rod. Usually, in order to facilitate itshandling, the raw material polycrystalline silicon is cut into cylindersof about 70 cm in length, and the mass (called silicon rods) is chargedin a crucible for melting and is molten therein. In this case, in orderto increase the efficiency of melting, it is generally performed tosuspend a silicon rod and introduce it into the remainder of a melt.

[0003] Heretofore, a silicon rod provided with a groove on the peripherythereof near its top is suspended by engaging it with a wire in thegroove. As a result, the rod excluding the upper portion thereof, i.e.,from a position several centimeters below the groove to the top of therod is molten, so that the efficiency of melting is insufficient. In thecase where many silicon rods are to be molten, each of the steps ofattaching a wire to the rod, charging the rod into a silicon melt, anddrawing up the remaining part of the rod must be repeated several times.This disadvantageously decreases the efficiency of melting operationconsiderably. To cope with this, a process for simultaneously suspendinga plurality of silicon rods has been proposed (cf. JP-A-09-255467).However, this process is not free of the defect in that the upperportion from a position neighboring the groove in the periphery of therod to its upper end makes a melting loss. In addition, a process isknown in which silicon rods are each provided with grooves around itsperiphery on both upper and lower ends, respectively, two such rods arebutted end-to-end, and an annular member having a U-shape cross-sectionis inserted into the upper and lower grooves to couple the rods to eachother (cf. JP-A-08-310892). However, this process has the problem ofinstability since it uses a coupling member that is inserted fromoutside in the groove on the rod on its top to engage it therein so thatthe coupling member could be disengaged when it would happen to be incontact with the exterior when the coupled rods are being transported orfitted to the melting apparatus.

[0004] In the case where a silicon rod made of polycrystalline siliconis processed so as to have a conventional suspending structure in itsend portion, annealing treatment intended to decrease residual stressmust be practiced to the rod in order to process it without damages.When a polycrystalline silicon rod is produced from trichlorosilane andhydrogen as the raw materials by the Siemens method, a temperaturedifference of 100° C. or more occurs between the central part of the rodand the surface part of the rod. This causes a difference in stressbetween the central part and the surface part, which difference instress remains in the rod as residual stress after completion of thereaction.

[0005] Accordingly, if the rod is processed to provide therein a groovewithout performing annealing treatment in advance, cracks tend to occurin the rod by residual stress, thereby damaging the processed portion ofthe rod. On the contrary, if the annealing treatment is practiced,contamination of metals from the heating source occurs unavoidably sothat the purity of polycrystalline silicon is decreased. Further, theanneal treatment needs heating at about 1,200° C., which is not onlytroublesome but also requires of an appliance that can afford topractice high temperature heating.

DISCLSURE OF THE INVENTION

[0006] The present invention is devoted to solve such problems asdescribed above, and an object of the present invention is to provide astructure that can enable stable and easy hanging silicon rods eachother.

[0007] Another object of the present invention is to provide a method ofprocessing silicon rods in a stable manner without performing annealingtreatment when such a coupling structure is to be processed.

[0008] That is, the present invention provides a silicon rod having thefollowing structure and method of processing it.

[0009] 1) A polycrystalline silicon rod having a structure for hangingof polycrystalline silicon rods to each other end-to-end, wherein anengaging groove is formed on at least one end face of the rods facing toeach other, the engaging groove being defined by a slit having a narrowwidth and an inner space larger than the width of the slit, being openon an end face of the rod and on a side face of the rod, and beingadapted for receiving a coupling member having both end portions largerthan the width of the slit, whereby being capable of coupling the rodsby fitting the coupling member into the respective engaging grooves ofthe rods facing to each other.

[0010] 2) A polycrystalline silicon rod obtained by entirely orpartially removing a peripheral portion from an end portion of the rodto leave a central portion, and processing the central portion.

[0011] 3) A polycrystalline silicon rod as described in the above item

[0012] 2), wherein both shoulder portions of the rod end portion areremoved to leave a central portion and an engaging grove is formed inthe central portion.

[0013] 4) A polycrystalline silicon rod as described in the above item2), wherein the peripheral portion is removed in an amount correspondingto 10 to 60% of a diameter of the rod end portion.

[0014] 5) A polycrystalline silicon rod having a structure for hangingof polycrystalline silicon rods to each other end-to-end, wherein aperipheral portion of the rod is entirely or partially removed to leavea central portion, and an engaging groove is formed on the centralportion, the engaging groove being defined by a slit having a narrowwidth and an inner space larger than the width of the slit, being openon an end face of the rod and on a side face of the rod, and beingadapted for receiving a coupling member having both end portions largerthan the width of the slit, whereby being capable of coupling the rodsby fitting the coupling member into the respective engaging grooves ofthe rods facing to each other.

[0015] 6) A polycrystalline silicon rod as described in the aboveitem 1) or 5), wherein the engaging groove has an inner space having aspherical, polygonal or dovetail groove-like shape.

[0016] 7) A method of processing a polycrystalline silicon rod,comprising entirely or partially removing a peripheral portion from anend portion of the rod to leave a central portion, and processing thecentral portion.

[0017] 8) A method of processing a polycrystalline silicon rod asdescribed in the above item 7), wherein both shoulder portions of a rodend portion are removed to leave the central portion, and an engaginggrove penetrating the cross section of the central portion is formedtherein.

[0018] A polycrystalline silicon rod according to the present inventionhas a structure for hanging of polycrystalline silicon rods to eachother end-to-end, wherein an engaging groove is formed on at least oneend face of the rods facing to each other, the engaging groove beingdefined by a slit having a narrow width and an inner space larger thanthe width of the slit, being open on an end face of the rod and on aside face of the rod, and being adapted for receiving a coupling memberhaving both end portions larger than the width of the slit, wherebybeing capable of coupling the rods by fitting the coupling member intothe respective engaging grooves of the rods facing to each other.Employment of this coupling structure eliminates a fear that thecoupling member easily comes off, and enables to engage the rods withstably and ease.

[0019] Further, according to the processing method of the presentinvention, a polycrystalline silicon rod can be subjected togroove-forming processing without annealing treatment at hightemperature, thereby being capable of preventing the contamination ofmetals due to the high temperature heating. This makes the apparatus forheating unnecessary, thereby being capable of processing speedily. Thus,the polycrystalline silicon rod subjected to the processing of thepresent invention minimizes the contamination of metals to obtain highpurity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1, FIG. 2, and FIG. 3 are partial views showing appearancesof coupling structure portions of a silicon rod;

[0021]FIG. 4 shows a partial appearance of coupling state of siliconrods, which are coupled vertically.

[0022]FIG. 5 is a diagram illustrating a state initiating a processingprocess of the present invention;

[0023]FIG. 6 is a diagram illustrating a procedure of processing processof the present invention;

[0024]FIG. 7 and FIG. 8 show processes for processing silicon rods tohave other shapes according to the present invention, in which FIG. 7 isa schematic appearance of a top end of the rod;

[0025]FIG. 8 are diagrams showing plane, front and side faces of the rodshown in FIG. 7;

[0026]FIG. 9 is a cross-sectional view showing an engaging grooveprocessed by the process of the present invention;

[0027]FIG. 10 shows a perspective appearance of the engaging grooveprocessed by the method of the present invention;

[0028]FIG. 11 is a plan view showing the engaging groove processed bythe method of the present invention; and

[0029]FIG. 12 is a diagram illustrating distribution of residual stressin the inside of a polycrystalline silicon rod.

BEST MODE FOR CARRYING OUT THE INVENTION

[0030] Hereinafter, the present invention will be described in detail byembodiments with reference to the attached drawings.

[0031] As illustrated, a silicon rod 10 of the present invention isprovided with an engaging groove 20 in at least one end portion thereof.The engaging groove is constituted by a slit 21 and an inner space 22.The slit 21 is a narrow groove, which opens on an end surface 16 and aside surface 17 of rod and extends toward the inside of the rod. Theinner space 22 is integrally formed in communication with the inwardlyextending slit 21. The inner space 22 is formed wider in width than thatof the groove of the slit 21, so that the space communicating with therod end surface 16 is formed narrow by the slit 21. The inner space 22at its side end opens on the side surface 17.

[0032] The inner space 22 shown in FIG. 1 is formed in the form of acylinder. However, the shape of the inner space 22 is not particularlylimited thereto. As shown in FIGS. 2 and 3, the shape of opening on therod side surface 17 may be polygonal or in the form of a dovetail grooveor any other shape as far as its width is greater than the width of theslit. The depth (D) of the slit 21, that is, the length of the slit 21until it reaches the inner space 22 is optional. In the case where theinner space 22 is cylindrical or in the form of a dovetail groove asshown in FIG. 1 or 2, the depth (D) of the slit 21 may be set tosubstantially zero (0) so that a portion of the inner space 22 candirectly open on the rod end surface 16. Furthermore, the length (L) ofthe slit 21 and inner space 22 is optional and may be any dimension asfar as the coupling member 26 can securely be engaged in the engaginggroove 26. Note that, in the example shown in the figure, the length (L)of the slit 21 and inner space 22 is set so that they reach near theaxis of the rod 10. However, that length (L) may be set to a dimensionso that they can extend horizontally across the rod along a diameterthereof. Thus, the coupling structure of the present invention may alsoinclude the structure in which a portion of the inner space 22 directlyopens on the rod end surface 16 or the structure in which the slit orinner space extends through the rod.

[0033] The engaging groove 20 is formed at least one end portion of thesilicon rod. As shown in FIG. 4, a silicon rod 18 to be attached to awire (not shown) suspending a rod of a melting apparatus is providedwith a groove 25 for winding a wire around it and with theabove-described engaging groove 20 in the lower end portion of the rod.A silicon rod 19 to be coupled to the silicon rod 18 is provided withthe engaging groove 20 according to the present invention in its upperend portion. Into the engaging groove 20 is inserted a coupling member26. The coupling member 26 is formed so as to have a greater width onits both end portions 26 a and 26 b than the width of the slit as isillustrated. The end portions 26 a and 26 b of the coupling member 26are inserted into the engaging grooves 20, 20 of the silicon rods 18 and19, respectively, from the openings on the side surfaces thereof to fitthem thereinto. This makes the coupling member 26 to be fitted throughthe openings in the end surfaces of the rods so that it can bridge theboth silicon rods.

[0034] The end portions 26 a and 26 b of the coupling member 26 are madewider than the width of the slit so that the end portions 26 a and 26 bare engaged in the end portions of the slits against the force exertedin the direction along the axis of the rod (force directed toward theend surface), which prevents the coupling member 26 from coming off fromthe engaging groove 20. As a result, the silicon rods can be coupled toeach other in a stable manner. Since the engaging groove 20 opens on therod side surface, the coupling member 26 can be inserted in the engaginggroove 20 with ease and also detached therefrom with ease. Furthermore,since the coupling rod 26 is engaged in the inside of the rod, there isno fear that the engaged portion contacts the exterior to be disengagedwhen the coupled rods are handled.

[0035]FIG. 4 illustrates an example of two silicon rods coupledend-to-end vertically but the coupling structure of the presentinvention is not limited thereto. For example, a plurality of siliconrods can be coupled and suspended as follows. That is, more than twosilicon rods are prepared, each of which is provided with theabove-described engaging groove 20 on each of the upper and lower endportions of the silicon rod, the silicon rods are coupled end-to-endthrough the engaging grooves 20. Then, the coupled silicon rods aresuspended vertically. The coupling structure of the present inventioncan be advantageously applied to silicon-silicon rods and in this caseit is preferred that the coupling member made of silicon be used.

[0036] By using the above-described coupling structure, a plurality ofsilicon rods can be coupled end-to-end and suspended vertically so thatthe efficiency of melting polycrystalline silicon can be increasedconsiderably. Since the coupling structure of the present invention isengaged in the inside of the rod, the state of engagement is stable andfurther, the operation is easy since the coupling member can be insertedfor engagement from the side surface of the rod.

[0037] Next, the processing process of the present invention and thesilicon rod subjected to the processing process will be described basedon the illustrated embodiment.

[0038] FIGS. 5 to 8 are diagrams illustrating the processing process ofthe present invention. FIGS. 9 to 11 are cross-sectional view, partialperspective view and plan view, respectively, showing the shape ofgroove (hole). FIG. 12 is a schematic diagram illustrating distributionof residual stress in the rod.

[0039] The processing process of the present invention and the rodsubjected thereto are featured by removing a peripheral portion of thepolycrystalline rod entirely or partially and subjecting the remainingcentral portion thereof to processing. More particularly, for example,the peripheral portion of the rod end portion is cut round along theperipheral surface to leave a cylindrical central portion or bothshoulder portions of a rod end portion is cut off to leave a protrudedstrip-like central portion, and then the remaining central portion isprocessed to provide an engaging groove and the like.

[0040] When a polycrystalline silicon rod is produced by the Siemensprocess, in which trichlorosilane and hydrogen as the raw materials areintroduced in a sealed vessel and the raw material gases are contactedwith the surface of a silicon seed rod heated to a high temperature byapplication of electric current to thermally decompose thetrichlorosilane, thereby depositing silicon, the central portion of therod has a temperature higher than that of the surface of the rod, sothat there is generated a difference in temperature as large as 100° C.or more. This results in a difference in stress between the centralportion and the surface portion, which difference remains in the rod asresidual stress after completion of the reaction.

[0041] More particularly, as shown in FIG. 12, always a compressionstress is exerted in the circumferential direction (direction θ),whereas in the radial direction (direction r) a compression stress isexerted in the central portion of the rod but a tensile stress isexerted in the peripheral portion of the rod. On the other hand, in theaxial direction (direction z), a tensile stress is exerted in thecentral portion of the rod but a compression stress is exerted in theperipheral portion of the rod. In the presence of such residualstresses, if the upper end portion of a silicon rod is processed to forma groove, a tensile stress is exerted in the range of the in the radialdirection (direction r) so that cracks tend to occur in the radialdirection and the rod could be broken easily.

[0042] Accordingly, in the present invention, making the best of thefact that always a compression stress is exerted in the circumferentialdirection, the peripheral portion 10 b of the rod 10 is removed alongthe circumferential direction as shown in FIG. 6 to decrease the tensilestress in the radial direction. Alternatively, as shown in FIG. 7, apart of the peripheral portion of the rod end portion, that is, bothshoulder portions 31 of the rod end portion is cut off to decrease thetensile stress in the radial direction. The portion to be removed issuitably a portion corresponding to 10 to 60% of the diameter. Thecentral portion 10 a or 30 left after the removal of the peripheralportion is mostly in the region where a compression stress is exerted,so that it will not be cracked when it is subjected to processing. Theremoved portion of less than 10% of the diameter of the rod is notdesirable since the portion of tensile stress remains to such an extentthat the influence of tensile stress cannot be excluded sufficiently. Onthe other hand, the removed portion of above 60% is not suitable sincethe central portion to be further processed is too small.

[0043] An example of processing process is illustrated in FIGS. 5 to 8.As shown in FIG. 5, a diamond wheel (i.e., a cutter provided with adiamond coating on the periphery) is applied to the periphery at an endportion of the polycrystalline silicon rod (silicon rod) 10. Then therod 10 and wheel 11 are rotated in reverse directions to polish theperipheral portion 10 b of the rod 10 to remove it. The length of theground portion 10 b in the axial direction may be determined properlydepending on the shape and depth of the groove to be processed. Themethod for removing the peripheral portion is not limited to grindingand other methods, for example, a method of cutting off the portionsurrounding the peripheral portion using a diamond saw or the like andthen optionally grinding the resultant circumferential surface using adiamond wheel to obtain a smooth surface may be used.

[0044] Next, the central portion 10 a after the centering is subjectedto groove forming processing. More particularly, for example, thecentral portion 10 a is drilled using a drill of a small diameter in theradial direction to bore a hole 14 of a small diameter. This operationis repeated in the axial direction from the upper end surface of thecentral portion 10 a to the lower portion of the ground portion to forma groove (slit) 12 communicating vertically. Then using a drill 15 oflarger diameter, a hole 13 is bored on the bottom portion of the groove(slit) 12 extending in the same direction to form an engaging groove 20including an inner space 13 larger than the groove (slit) 12 andcommunicating therewith.

[0045] Furthermore, as shown in FIGS. 7 and 8, the peripheral portion ofthe rod end portion may be removed. More particularly, the shoulderportions 31 on the both sides of the upper end portion of the rod 10 areremoved to leave a central portion 30. In the cut surface of the centralportion 30 is provided an engaging groove 32, through which a slit 33 ofa narrower width is integrally formed vertically. The engaging groove 32may be provided as passing through the central portion 30 or as is shownin FIG. 8, it does not penetrate the central portion 30 but may beformed partway.

[0046] As described above, the engaging grooves 20 and 32 are formed byslits 12 and 33 and inner space (hole). The passage leading to the upperend surface of the rod is formed by the slits 12 and 33, which arenarrower, and the inner space from the bottom portion of the slit to thecentral portion is formed larger. The inner space (hole) opens on theside surface of the rod. In the example illustrated, the inner space ofthe engaging grooves 20 and 30 are formed cylindrical. However, they maybe polygonal or dovetail shape in cross section. Also, any other shapesmay be used as far as they are wider than the slits 12 and 33. The depth(length to the inside of the engaging groove) and length in the radialdirection of the slits 12 and 33 are optional and may be any dimensionas far as the coupling member can be firmly fitted in the engaginggrooves 20 and 30. As shown in FIG. 9, the border portion between thegroove (slit) 12 and the inner space may preferably be of a structurethat can prevent damages of a corner portion by providing a taper θ withthe corner portion.

[0047] What is shown in FIG. 10 is an example of the shape of the rodend portion as shown in FIG. 6, in which the engaging groove 20 passesthrough the central portion 10 a of the rod in the radial direction. Thelength of the engaging groove 20 in the radial direction may be partwayof the central portion 10 a as shown in FIG. 11.

[0048] The engaging grooves 20 and 30 as described above are formed inat least one end portion of the silicon rod 10, or in both opposing endsurfaces of a pair of silicon rods butted one against another and therods are coupled to each other end-to-end by means of a coupling member(not shown) that is fitted in the engaging grooves 20 and 30 and thecoupled rods are suspended. The coupling member has both ends largerthan the width of the slits 12 and 33, and the end portions thereof areinserted in the engaging grooves 20 and 30 in the silicon rods,respectively. Since the end portions of the coupling member are eachgreater than the width of the slits, the end portions can couple thesilicon rods 10 to each other without coming off from the slit groove.Since the engaging grooves 20 and 30 are opened toward the side surfaceof the rod, the coupling member can be inserted in the engaging grooves20 and 30 with ease and also detached with ease. Furthermore, since thecoupling member engages in the inside of the engaging grooves 20 and 30,there is no possibility that the engaged portion will contact theexterior and come off.

INDUSTRIAL APPLICABILITY

[0049] A polycrystalline silicon rod according to present invention hasa structure for hanging of polycrystalline silicon rods to each otherend-to-end, so that the efficiency of melting polycrystalline siliconcan be increased considerably. According to the polycrystallineprocessing process of the present invention and the polycrystallinesilicon rod formed by the processing process, processing for forminggrooves for coupling silicon rods made of polycrystalline silicon toeach other can be performed without subjecting the silicon rods toannealing treatment so that contamination with metal can be avoided.Further, since the annealing treatment is unnecessary, the processingprocess can be simplified considerably so that processing for forminggrooves and the like can be performed speedily. Furthermore, no heatingappliance for annealing treatment is necessary so that processing costscan be reduced.

1. A polycrystalline silicon rod having a structure for hanging ofpolycrystalline silicon rods to each other end-to-end, wherein anengaging groove is formed on at least one end face of the rods facing toeach other, the engaging groove being defined by a slit having a narrowwidth and an inner space larger than the width of the slit, being openon an end face of the rod and on a side face of the rod, and beingadapted for receiving a coupling member having both end portions largerthan the width of the slit, whereby being capable of coupling the rodsby fitting the coupling member into the respective engaging grooves ofthe rods facing to each other.
 2. A polycrystalline silicon rod obtainedby entirely or partially removing a peripheral portion from an endportion of the rod to leave a central portion, and processing thecentral portion.
 3. A polycrystalline silicon rod according to claim 2,wherein both shoulder portions of the rod end portion are removed toleave a central portion and an engaging grove is formed in the centralportion.
 4. A polycrystalline silicon rod according to claim 2, whereinthe peripheral portion is removed in an amount corresponding to 10 to60% of a diameter of the rod end portion.
 5. A polycrystalline siliconrod having a structure for hanging of polycrystalline silicon rods toeach other end-to-end, wherein a peripheral portion of the rod isentirely or partially removed to leave a central portion, and anengaging groove is formed on the central portion, the engaging groovebeing defined by a slit having a narrow width and an inner space largerthan the width of the slit, being open on an end face of the rod and ona side face of the rod, and being adapted for receiving a couplingmember having both end portions larger than the width of the slit,whereby being capable of coupling the rods by fitting the couplingmember into the respective engaging grooves of the rods facing to eachother.
 6. A polycrystalline silicon rod according to claim 1 or 5,wherein the engaging groove has an inner space having a spherical,polygonal or dovetail groove-like cross sectional shape.
 7. A method ofprocessing a polycrystalline silicon rod, comprising entirely orpartially removing a peripheral portion from an end portion of the rodto leave a central portion, and processing the central portion.
 8. Amethod of processing a polycrystalline silicon rod according to claim 7,wherein both shoulder portions of a rod end portion are removed to leavethe central portion, and an engaging grove penetrating the cross sectionof the central portion is formed therein.